sd-id128: introduce ID128_REFUSE_NULL flag

src/libsystemd/sd-id128/id128-util.c

@@ -43,6 +43,7 @@ bool id128_is_valid(const char *s) {
 
 int id128_read_fd(int fd, Id128Flag f, sd_id128_t *ret) {
         char buffer[SD_ID128_UUID_STRING_MAX + 1]; /* +1 is for trailing newline */
+        sd_id128_t id;
         ssize_t l;
         int r;
 
@@ -98,8 +99,18 @@ int id128_read_fd(int fd, Id128Flag f, sd_id128_t *ret) {
                 return -EUCLEAN;
         }
 
-        r = sd_id128_from_string(buffer, ret);
-        return r == -EINVAL ? -EUCLEAN : r;
+        r = sd_id128_from_string(buffer, &id);
+        if (r == -EINVAL)
+                return -EUCLEAN;
+        if (r < 0)
+                return r;
+
+        if (FLAGS_SET(f, ID128_REFUSE_NULL) && sd_id128_is_null(id))
+                return -ENOMEDIUM;
+
+        if (ret)
+                *ret = id;
+        return 0;
 }
 
 int id128_read_at(int dir_fd, const char *path, Id128Flag f, sd_id128_t *ret) {
@@ -123,6 +134,9 @@ int id128_write_fd(int fd, Id128Flag f, sd_id128_t id) {
         assert(fd >= 0);
         assert(IN_SET((f & ID128_FORMAT_ANY), ID128_FORMAT_PLAIN, ID128_FORMAT_UUID));
 
+        if (FLAGS_SET(f, ID128_REFUSE_NULL) && sd_id128_is_null(id))
+                return -ENOMEDIUM;
+
         if (FLAGS_SET(f, ID128_FORMAT_PLAIN)) {
                 assert_se(sd_id128_to_string(id, buffer));
                 sz = SD_ID128_STRING_MAX;

src/libsystemd/sd-id128/id128-util.h

@@ -17,6 +17,7 @@ typedef enum Id128Flag {
         ID128_FORMAT_ANY    = ID128_FORMAT_PLAIN | ID128_FORMAT_UUID,
 
         ID128_SYNC_ON_WRITE = 1 << 2, /* Sync the file after write. Used only when writing an ID. */
+        ID128_REFUSE_NULL   = 1 << 3, /* Refuse all zero ID with -ENOMEDIUM. */
 } Id128Flag;
 
 int id128_read_fd(int fd, Id128Flag f, sd_id128_t *ret);

src/libsystemd/sd-id128/sd-id128.c

@@ -126,12 +126,9 @@ _public_ int sd_id128_get_machine(sd_id128_t *ret) {
         int r;
 
         if (sd_id128_is_null(saved_machine_id)) {
-                r = id128_read("/etc/machine-id", ID128_FORMAT_PLAIN, &saved_machine_id);
+                r = id128_read("/etc/machine-id", ID128_FORMAT_PLAIN | ID128_REFUSE_NULL, &saved_machine_id);
                 if (r < 0)
                         return r;
-
-                if (sd_id128_is_null(saved_machine_id))
-                        return -ENOMEDIUM;
         }
 
         if (ret)
@@ -144,14 +141,11 @@ _public_ int sd_id128_get_boot(sd_id128_t *ret) {
         int r;
 
         if (sd_id128_is_null(saved_boot_id)) {
-                r = id128_read("/proc/sys/kernel/random/boot_id", ID128_FORMAT_UUID, &saved_boot_id);
+                r = id128_read("/proc/sys/kernel/random/boot_id", ID128_FORMAT_UUID | ID128_REFUSE_NULL, &saved_boot_id);
                 if (r == -ENOENT && proc_mounted() == 0)
                         return -ENOSYS;
                 if (r < 0)
                         return r;
-
-                if (sd_id128_is_null(saved_boot_id))
-                        return -ENOMEDIUM;
         }
 
         if (ret)